8365057: Add support for java.util.concurrent lock information to Thread.dump_to_file

Co-authored-by: Alex Menkov <[email protected]>
Co-authored-by: Alan Bateman <[email protected]>
Reviewed-by: sspitsyn, alanb

Author: Alex Menkov

src/hotspot/share/services/threadService.cpp

@@ -1161,9 +1161,11 @@ class GetThreadSnapshotHandshakeClosure: public HandshakeClosure {
     Type _type;
     // park blocker or an object the thread waiting on/trying to lock
     OopHandle _obj;
+    // thread that owns park blocker object when park blocker is AbstractOwnableSynchronizer
+    OopHandle _owner;
 
-    Blocker(Type type, OopHandle obj): _type(type), _obj(obj) {}
-    Blocker(): _type(NOTHING), _obj(nullptr) {}
+    Blocker(Type type, OopHandle obj): _type(type), _obj(obj), _owner() {}
+    Blocker(): _type(NOTHING), _obj(), _owner() {}
 
     bool is_empty() const {
       return _type == NOTHING;
@@ -1198,6 +1200,7 @@ class GetThreadSnapshotHandshakeClosure: public HandshakeClosure {
       delete _locks;
     }
     _blocker._obj.release(oop_storage());
+    _blocker._owner.release(oop_storage());
   }
 
 private:
@@ -1300,6 +1303,13 @@ class GetThreadSnapshotHandshakeClosure: public HandshakeClosure {
     oop park_blocker = java_lang_Thread::park_blocker(_thread_h());
     if (park_blocker != nullptr) {
       _blocker = Blocker(Blocker::PARK_BLOCKER, OopHandle(oop_storage(), park_blocker));
+      if (park_blocker->is_a(vmClasses::java_util_concurrent_locks_AbstractOwnableSynchronizer_klass())) {
+        // could be stale (unlikely in practice), but it's good enough to see deadlocks
+        oop ownerObj = java_util_concurrent_locks_AbstractOwnableSynchronizer::get_owner_threadObj(park_blocker);
+        if (ownerObj != nullptr) {
+          _blocker._owner = OopHandle(oop_storage(), ownerObj);
+        }
+      }
     }
 
     ResourceMark rm(current);
@@ -1381,6 +1391,7 @@ class jdk_internal_vm_ThreadSnapshot: AllStatic {
   static int _locks_offset;
   static int _blockerTypeOrdinal_offset;
   static int _blockerObject_offset;
+  static int _parkBlockerOwner_offset;
 
   static void compute_offsets(InstanceKlass* klass, TRAPS) {
     JavaClasses::compute_offset(_name_offset, klass, "name", vmSymbols::string_signature(), false);
@@ -1390,6 +1401,7 @@ class jdk_internal_vm_ThreadSnapshot: AllStatic {
     JavaClasses::compute_offset(_locks_offset, klass, "locks", vmSymbols::jdk_internal_vm_ThreadLock_array(), false);
     JavaClasses::compute_offset(_blockerTypeOrdinal_offset, klass, "blockerTypeOrdinal", vmSymbols::int_signature(), false);
     JavaClasses::compute_offset(_blockerObject_offset, klass, "blockerObject", vmSymbols::object_signature(), false);
+    JavaClasses::compute_offset(_parkBlockerOwner_offset, klass, "parkBlockerOwner", vmSymbols::thread_signature(), false);
   }
 public:
   static void init(InstanceKlass* klass, TRAPS) {
@@ -1420,9 +1432,10 @@ class jdk_internal_vm_ThreadSnapshot: AllStatic {
   static void set_locks(oop snapshot, oop locks) {
     snapshot->obj_field_put(_locks_offset, locks);
   }
-  static void set_blocker(oop snapshot, int type_ordinal, oop lock) {
+  static void set_blocker(oop snapshot, int type_ordinal, oop lock, oop owner) {
     snapshot->int_field_put(_blockerTypeOrdinal_offset, type_ordinal);
     snapshot->obj_field_put(_blockerObject_offset, lock);
+    snapshot->obj_field_put(_parkBlockerOwner_offset, owner);
   }
 };
 
@@ -1434,6 +1447,7 @@ int jdk_internal_vm_ThreadSnapshot::_stackTrace_offset;
 int jdk_internal_vm_ThreadSnapshot::_locks_offset;
 int jdk_internal_vm_ThreadSnapshot::_blockerTypeOrdinal_offset;
 int jdk_internal_vm_ThreadSnapshot::_blockerObject_offset;
+int jdk_internal_vm_ThreadSnapshot::_parkBlockerOwner_offset;
 
 oop ThreadSnapshotFactory::get_thread_snapshot(jobject jthread, TRAPS) {
   ThreadsListHandle tlh(THREAD);
@@ -1559,7 +1573,8 @@ oop ThreadSnapshotFactory::get_thread_snapshot(jobject jthread, TRAPS) {
   jdk_internal_vm_ThreadSnapshot::set_stack_trace(snapshot(), trace());
   jdk_internal_vm_ThreadSnapshot::set_locks(snapshot(), locks());
   if (!cl._blocker.is_empty()) {
-    jdk_internal_vm_ThreadSnapshot::set_blocker(snapshot(), cl._blocker._type, cl._blocker._obj.resolve());
+    jdk_internal_vm_ThreadSnapshot::set_blocker(snapshot(),
+        cl._blocker._type, cl._blocker._obj.resolve(), cl._blocker._owner.resolve());
   }
   return snapshot();
 }

src/java.base/share/classes/jdk/internal/vm/ThreadDumper.java

@@ -205,7 +205,10 @@ private static boolean dumpThread(Thread thread, TextWriter writer) {
                 // park blocker
                 Object parkBlocker = snapshot.parkBlocker();
                 if (parkBlocker != null) {
-                    writer.println("    - parking to wait for " + decorateObject(parkBlocker));
+                    String suffix = (snapshot.parkBlockerOwner() instanceof Thread owner)
+                            ? ", owner #"  + owner.threadId()
+                            : "";
+                    writer.println("    - parking to wait for " + decorateObject(parkBlocker) + suffix);
                 }
 
                 // blocked on monitor enter or Object.wait
@@ -335,6 +338,9 @@ private static boolean dumpThread(Thread thread, JsonWriter jsonWriter) {
             // parkBlocker is an object to allow for exclusiveOwnerThread in the future
             jsonWriter.startObject("parkBlocker");
             jsonWriter.writeProperty("object", Objects.toIdentityString(parkBlocker));
+            if (snapshot.parkBlockerOwner() instanceof Thread owner) {
+                jsonWriter.writeProperty("owner", owner.threadId());
+            }
             jsonWriter.endObject();
         }
 

src/java.base/share/classes/jdk/internal/vm/ThreadSnapshot.java

@@ -44,6 +44,8 @@ class ThreadSnapshot {
     // an object the thread is blocked/waiting on, converted to ThreadBlocker by ThreadSnapshot.of()
     private int blockerTypeOrdinal;
     private Object blockerObject;
+    // the owner of the blockerObject when the object is park blocker and is AbstractOwnableSynchronizer
+    private Thread parkBlockerOwner;
 
     // set by ThreadSnapshot.of()
     private ThreadBlocker blocker;
@@ -70,8 +72,11 @@ static ThreadSnapshot of(Thread thread) {
             snapshot.locks = EMPTY_LOCKS;
         }
         if (snapshot.blockerObject != null) {
-            snapshot.blocker = new ThreadBlocker(snapshot.blockerTypeOrdinal, snapshot.blockerObject);
+            snapshot.blocker = new ThreadBlocker(snapshot.blockerTypeOrdinal,
+                                                 snapshot.blockerObject,
+                                                 snapshot.parkBlockerOwner);
             snapshot.blockerObject = null; // release
+            snapshot.parkBlockerOwner = null;
         }
         return snapshot;
     }
@@ -104,6 +109,13 @@ Object parkBlocker() {
         return getBlocker(BlockerLockType.PARK_BLOCKER);
     }
 
+    /**
+     * Returns the owner of the parkBlocker if the parkBlocker is an AbstractOwnableSynchronizer.
+     */
+    Thread parkBlockerOwner() {
+        return (blocker != null && blocker.type == BlockerLockType.PARK_BLOCKER) ? blocker.owner : null;
+    }
+
     /**
      * Returns the object that the thread is blocked on.
      * @throws IllegalStateException if not in the blocked state
@@ -211,11 +223,11 @@ Object lockObject() {
         }
     }
 
-    private record ThreadBlocker(BlockerLockType type, Object obj) {
+    private record ThreadBlocker(BlockerLockType type, Object obj, Thread owner) {
         private static final BlockerLockType[] lockTypeValues = BlockerLockType.values(); // cache
 
-        ThreadBlocker(int typeOrdinal, Object obj) {
-            this(lockTypeValues[typeOrdinal], obj);
+        ThreadBlocker(int typeOrdinal, Object obj, Thread owner) {
+            this(lockTypeValues[typeOrdinal], obj, owner);
         }
     }
 

src/jdk.management/share/classes/com/sun/management/doc-files/threadDump.schema.json

@@ -78,6 +78,10 @@
                               "description": "The blocker object responsible for the thread parking."
                             }
                           },
+                          "owner": {
+                            "type": "string",
+                            "description": "The thread identifier of the owner when the parkBlocker is an AbstractOwnableSynchronizer."
+                          }
                           "required": [
                             "object"
                           ]
@@ -115,9 +119,9 @@
                                 "items": {
                                   "type": [
                                     "string",
-                                    null
+                                    "null"
                                   ],
-                                  "description": "The object for which the monitor is owned by the thread, null if eliminated"
+                                  "description": "The object for which the monitor is owned by the thread, null if eliminated."
                                 }
                               }
                             },

test/jdk/com/sun/management/HotSpotDiagnosticMXBean/DumpThreads.java

@@ -23,7 +23,7 @@
 
 /*
  * @test
- * @bug 8284161 8287008 8309406 8356870
+ * @bug 8284161 8287008 8309406 8356870 8365057
  * @summary Basic test for com.sun.management.HotSpotDiagnosticMXBean.dumpThreads
  * @requires vm.continuations
  * @modules java.base/jdk.internal.vm jdk.management
@@ -425,7 +425,9 @@ void testParkedThread(ThreadFactory factory, boolean pinned) throws Exception {
             ThreadFields fields = findThread(tid, lines);
             assertNotNull(fields, "thread not found");
             assertEquals("WAITING", fields.state());
-            assertTrue(contains(lines, "- parking to wait for <java.util.concurrent.locks.ReentrantLock"));
+            String line = find(lines, "- parking to wait for <java.util.concurrent.locks.ReentrantLock");
+            assertNotNull(line, "parking to wait line not found");
+            assertTrue(line.endsWith(" owner #" + Thread.currentThread().threadId()));
 
             // thread dump in JSON format should include thread in root container
             ThreadDump threadDump = dumpThreadsToJson();
@@ -440,6 +442,12 @@ void testParkedThread(ThreadFactory factory, boolean pinned) throws Exception {
             String parkBlocker = ti.parkBlocker();
             assertNotNull(parkBlocker);
             assertTrue(parkBlocker.contains("java.util.concurrent.locks.ReentrantLock"));
+
+            // the owner of the parkBlocker should be the current thread
+            long ownerTid = ti.parkBlockerOwner().orElse(-1L);
+            assertNotEquals(-1L, ownerTid, "parkBlockerOwner not found");
+            assertEquals(Thread.currentThread().threadId(), ownerTid);
+
             if (pinned) {
                 long carrierTid = ti.carrier().orElse(-1L);
                 assertNotEquals(-1L, carrierTid, "carrier not found");
@@ -684,6 +692,16 @@ private boolean contains(List<String> lines, String text) {
                 .anyMatch(l -> l.contains(text));
     }
 
+    /**
+     * Finds the line of a plain text thread dump containing the given text.
+     */
+    private String find(List<String> lines, String text) {
+        return lines.stream().map(String::trim)
+                .filter(l -> l.contains(text))
+                .findAny()
+                .orElse(null);
+    }
+
     /**
      * Dump threads to a file in plain text format, return the lines in the file.
      */

test/lib/jdk/test/lib/threaddump/ThreadDump.java

@@ -296,6 +296,16 @@ public String parkBlocker() {
             return getStringProperty("parkBlocker", "object");
         }
 
+        /**
+         * Returns the owner of the parkBlocker if the parkBlocker is an AbstractOwnableSynchronizer.
+         */
+        public OptionalLong parkBlockerOwner() {
+            String owner = getStringProperty("parkBlocker", "owner");
+            return (owner != null)
+                    ? OptionalLong.of(Long.parseLong(owner))
+                    : OptionalLong.empty();
+        }
+
         /**
          * Returns the object that the thread is blocked entering its monitor.
          */